Stop passing register descriptors everywhere - use integer IDs

[navnavnav]

At startup, Bloom extracts all register information from the relevant TDF, and constructs a TargetRegisterDescriptor for each register.

Whenever we want to do something with a register, like read its value, we pass the TargetRegisterDescriptor to the TargetControllerService, where it eventually gets copied. This copying can be expensive, as the TargetRegisterDescriptor contains multiple std::strings.

We shouldn't be using TargetRegisterDescriptor objects as register IDs. Instead, we should introduce an integer ID in TargetRegisterDescriptor, which should then be used to reference registers throughout Bloom.

Register descriptors should still be included in the TargetDescriptor.

[navnavnav]

This is done. The changes have been merged into develop and will be included in the v1.0.0 release.

Closing this now.